Coroutines in sabre/event is a feature that can improve your Promise-based code.

It comes in the form of a single function, that takes a generator as an argument. The generator can then yield promises. The coroutine function will automatically resume the function when the promise has resolved.

If the promise rejected, an exception will be thrown in the generator.

To illustrate this, an example will work better.


$promise = someAsyncOperation();
$promise->then(function($result)) {

    return anotherAsyncOperation();

->then( function($result) {

    return lastAsyncOperation();

->then (function($result)) {

    echo $result, "\n";

->otherwise(function($reason) {

    echo $reason, "\n";



The following code is equivalent:

use Sabre\Event;

Event\coroutine(function() {

    try {

        $result = yield someAsyncOperation();
        $result = yield anotherAsyncOperation();
        $result = yield lastAsyncOperation();
        echo $result;

    } catch (\Exception $reason) {

        echo $reason;



Tips and tricks

The coroutines itself also returns a promise. This promise will resolve with the value you returned from the coroutine.

This allows you to for example call wait() to turn a large asynchronous process into a blocking one:

use Sabre\Event;

Event\coroutine(function() {

    /* ... */


It's possible to call different coroutines from within your own coroutine easily as well:

use Sabre\Event;

Event\coroutine(function() {

    yield from $anotherGenerator;